Radiation Biology Flashcards
radiation biology
portion of science which studies the effects of ionizing radiation on living organisms
how do we know that radiation affects living organisms
early pioneers
1925 factory workers
nuclear bomb
spills and disasters
two mechanisms of radiation injury
ionization
free radical formation
ionization
results in formation of a positive atom and dislodged negative electron
dislodged electron interact with other atoms within tissues
compton scatter
when an x-ray photon collides with an outer-shell electron and ejects the electron from its orbit
formation of free radicals
x-ray photons ionizes H2O
hydrogen and hydroxyl free radicals
what is a free radical
an uncharged atom that exists with a single unpaired electron in its outermost shell: reactive and unstable
formation of free radicals Part A
x-ray photons interact with water in cells
ionization occurs
resulting in free radical formation
formation of free radicals Part B
free radicals
combine to form
toxins such as H2O2 (hydrogen peroxide)
damage to living tissue caused by exposure to ionizing radiation may result from
a direct hit and absorption of an x-ray photon within a cell
absorption of an x-ray photon by water within a cell accompanied by free radical formation
theories of radiation injury
direct theory and indirect theory
direct theory
cell damage results when ionizing radiation directly hits critical area within the cell
occurs infrequently
indirect theory
x-rays photons are absorbed within the cell and cause the formation of toxins which damage the cell
-when photons are absorbed by water within a cell, free radical formation results
-free radicals combine to form toxins that damage cells
dose-response curve
used to correlate the damage of tissue with the does of radiation received
liner nonthreshold relationship
stochastic radiation effects
direct function of the dose
no dose threshold; effects do not depend on magnitude of absorbed does
nonstochastic radiation effects
have a threshold and increase severity with increasing absorbed dose
occur after threshold of exposure has been exceeded
cause significant cell damage
sequence of radiation injury
latent period: time between exposure and observable clinical signs, depends of dose of radiation
period of injury: a variety of cellular injuries may result
recovery period: cells can repair the damage caused by radiation
cumulative effects: effects of radiation exposure are additive, unrepaired damage accumulates in tissues
determining factors of radiation injury
total dose
dose rate
amount of tissue irradiated
cell sensitivity
age
short term effects
not applicable to dentistry
long term effects
small doses absorbed over a long period of time
effects seen after years, decades, generations
somatic effects
all cells in body except reproductive cells
produce poor health in irradiated individual
cancer, leukemia, cataracts
genetic effects
reproductive cells
not seen in exposed individual
passed on to future generations
genetic damage cannot be repaired
radiosensitive cells
blood cells
immature reproductive cells
young bone cells
small lymphocyte
radioresistant cells
bone cells
muscle cells
nerve cells
